Method for wet etching of high k thin film at low temperature

ABSTRACT

The present invention discloses an electrode structure of a light emitted diode and manufacturing method of the electrodes. After formed a pn junction of a light emitted diode on a substrate, a layer of SiO2 is deposited on the periphery of the die of the LED near the scribe line of the wafer, then a transparent conductive layer is deposited blanketly, then a layer of gold or AuGe etc. is formed with an opening on the center of the die. After forming alloy with the semiconductor by heat treatment to form ohmic contact, a strip of aluminum (Al) is formed on one side of the die on the front side for wire bonding and to be the positive electrode of the LED. The negative electrode is formed on the substrate by metal contact. Another form of the electrode structure of the present invention is making both the positive and negative electrodes on the front side of the LED by etching the p-type semiconductor of the pn junction and forming a strip of negative electrode on the n-type semiconductor, the positive electrode is formed on the p-type semiconductor.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor d vice manufacturing method and more particularly, to a method for wet etching of high k thin film at low temperature.

[0003] 2. Description of Relative Prior Art

[0004] The recent development of semiconductor such as CMOS logic device or dynamic random access memory (DRAM), is preferable to increase the integration, increase the capacity, decrease the driving voltage etc., to meet the requirement of high speed, less delay. The design rule is more and more quickly reduced. It is a result that the thickness of the gate oxide is decreasing and approaching 60A or less. The fabrication process is more difficult to control. In a capacitor of a DRAM, a silicon dioxide insulator or an oxide-nitride-oxide (ONO) can not satisfy the need of the memory charge capacity, it is a trend that high dielectric film is used as the insulating film of a capacitor to replace the silicon dioxide or ONO. Recently, as the design rule approach 0.18 μm, there are lots of gate dielectric material can be used. The main requirement is: high dielectric, low leakage current, easy to etch and less contamination to the active area, etc. The most preferred material is Hafnium oxide (HfO₂) or Zirconium oxide (ZrO₂). Although they have an idea dielectric constant of 15-25, and more stable that they do not diffuse into the silicon active area, and the leakage current is less, but it is not easy to be etched. The experiment data is shown in Table 1. TABLE 1 Chemical Etch rate of HfO₂ (Å/min) Pure HClO₄ 0.3 Pure H₂SO₄(at 160° C.) 1.25-5.25 Pure H₃PO₄(at 80° C.) 0 BOE 20 Pure (COOH)₂ 0-2 Pure HCl   0-0.9 Pure HBr 2.5-10  Pure HI 0 Pure HF 101 Pure H₂O₂ 0 TMAH 0.4

[0005] From Table 1, we know that etching with Sulfuric acid (H₂SO₄) need to heat up to 160° C. and the etch rate is only 5 Å/min, the others like Phosphoric acid (H₃PO₄), acitic acid (COOH)₂, Hydrochloric acid (HCl), Hydro Bromide acid (HBr), Hydro iodine acid (HI), and pure HClO₄, has etch rate near zero. Although BOE and HF has etch rate of 20 Å/min and 100 Å/min respectively, but cannot be used since they also etch silicon dioxide. Poor selectivity of dry etching causes leakage current, which due to defects on the surface of the source/drain. So it needs to develop a new technique to replace wet etching by hot sulfuric acid and dry etching techniques.

[0006]FIG. 1 shows the cross section view before etching the gate dielectric of a CMOS device using Hafnium oxide (HfO₂) as the gate dielectric. Isolation 4 is formed on a silicon wafer 1 by LOCOS or STI, then using lithography and ion implantation to form a p-well 2 and n-well 3, after deposited Hafnium oxide film 5, poly-Si 6 and tungsten silicide or other silicide 7 formed a gate 9, the Hafnium oxide is now using as the etch stop. Then by using lithography and ion implantation to form a lightly doped n⁻ source/drain area 10 and p⁻ source/drain area 11. Refer to FIG. 2, by using lithography and ion implantation technique to form heavily doped n⁺ and p⁺ source/drain 12,13, thus form a LDD structure. Now the hafnium oxide has not etched away and is used as the buffer layer of ion implantation to prevent defects form on the surface of silicon. Finally, by using dry etching to remove the hafnium oxide above the source/drain area. The un-doped silicon glass (USG) and the silicon above the source/drain may form defects 14 since the selectivity is not high enough. After the process is completed the leakage current of the device will increase. The same reason is applied to the etching of the dielectric film of a DRAM, it may hurt the lower electrode and inter-metal-dielectric (IMD). Alternatively, if we use wet etching by hot sulfuric acid, the selectivity is good, but the etch rate is very low and need high temperature endurable equipments. It is preferred to develop a wet etch method at low temperature to improve the yield of production.

SUMMARY OF THE INVENTION

[0007] It is an object of the present invention to provide a method of wet etching a high k film and high k gate dielectric of a semiconductor device.

[0008] Another object of the present invention is to provide a method of wet etching a high k film which has high selectivity with respect to silicon dioxide (SiO₂), un-doped silicon glass (USG) and bulk silicon to reduced defects on USG in the isolation region, poly-Si gate and silicon of source/drain region, so that the leakage current and topology can be reduced.

[0009] The third object of the present invention is to provide a wet etch method at low temperature, which has acceptable etch rate, and the processing time can be reduced to increase throughput. In order to achieve the above objects, according to the first aspect of the present invention, a method using hydrofluoric acid (HF) and perchloric acid (HClO₄) (or perbromic acid HBrO₄, periodic acid HIO₄) mixture for etching the high k film on silicon dioxide (SiO₂) or poly-Si, the volume ratio is between 1:50 to 1:5000, the better is 1:1000 to 1:2500, at low temperature (0

to 100

), the etch rate of high k film is more than 10A/min. However the etch rate of SiO₂, USG and poly-Si is below 10A/min, the selectivity is good enough.

[0010] According to the second aspect of the present invention is to provide a method for manufacturing CMOS logic devices with high k gate dielectric film. After the gate, the lightly doped source/drain and the side-well of the gate has been formed, using HF and HClO₄ (or HBrO₄, HIO₄) mixture to etch the high k gate dielectric on the source/drain, would not hurt the USG in the shallow trench isolation region, the silicon surface of the source/drain region, the poly-Si gate and the metal gate or refractory metal silicide of the gate.

[0011] According to the third aspect of the present invention, is to provide a method for manufacturing DRAM with high k capacitor. After completed forming the transistor and lower electrode of a DRAM, and have deposited high k film as capacitor dielectric on the lower electrode, protect the bottom electrode and the high k film with photo resist, then remove the high k film by wet etch using HF and perchloric acid (HClO₄) (or perbromic acid HBrO₄, periodic acid HIO₄) mixture at low temperature (0

to 100

), very good etch pattern can be obtained, the etching process will not form defect on the BPSG or PSG under the high k film. The etch rate of high k film is above 10A/min, but the etch rate of BPSG or PSG is under 10A/min.

[0012] According to the fourth aspect of the present invention, is to provide a method for manufacturing high k capacitors. After a blanket deposition of high k dielectric film on the substrate having a lower electrode, protect the lower electrode and high k film on the lower electrode with photo-resist, then remove the high k film by wet etch using HF and perchloric acid (or perbromic acid HBrO₄, periodic acid HIO₄) mixture at low temperature (0

to 100

). This etching process will not damage the silicon substrate or the isolation silicon dioxide.

BRIEF DESCRIPTION OF THE DRAWING

[0013]FIG. 1 is a cross section view of a CMOS after the front-end process has formed nitride side-wall of the gate and before etching the high k film of the prior art;

[0014]FIG. 2 is a cross section view of a CMOS after the front-end process has formed the heavily doped source/drain and etched away the high k film above the source/drain of the prior art;

[0015]FIG. 3 is a graph of selectivity vs. different volume ratio of HF and HClO₄ for etching HfO₂ and USG;

[0016]FIG. 4 is a graph of etch rate vs. different volume ratio of HF and HClO₄ for etching high k dielectric (HfO₂), USG and poly-Si;

[0017]FIG. 5 is a cross section view of a CMOS logic device after the process is completed;

[0018]FIG. 6 is a cross section view of a CMOS substrate;

[0019]FIG. 7 is a cross section view after deposition of high k film (HfO₂) and poly-Si;

[0020]FIG. 8 is a cross section view after forming heavily doped n⁺ poly-Si;

[0021]FIG. 9 is a cross section view after forming heavily doped p⁺ poly-Si;

[0022]FIG. 10 is a cross section view after deposition of tungsten silicide;

[0023]FIG. 11 is a cross section view after forming the gate by etching the tungsten silicide and poly-Si;

[0024]FIG. 12 is a cross section view after forming the lightly-doped n⁻ source/drain;

[0025]FIG. 13 is a cross section view after forming the lightly-doped p⁻ source/drain;

[0026]FIG. 14 is a cross section view after deposition of Si₃N₄ and anisotropic etching;

[0027]FIG. 15 is a cross section view after deposition of high k (HfO₂) on the stack electrode (lower electrode) of a DRAM according to the present invention;

[0028]FIG. 16 is a cross section view after removed the high k (HfO₂) on the source/drain region with HF and HClO₄ mixture according the present invention;

[0029]FIG. 17 is a cross section view after the process of a DRAM is completed according to the present invention;

DETAILED DESCRIPTION OF THE PREFERED EMBODIMENT

[0030] Preferred embodiment of the present invention will now be explained with reference to the accompanying drawings

[0031] First Embodiment

[0032] The etching of high k material (HfO₂) film has been studied with different solution by the inventers. All the HfO₂ film is deposited by Physical vapor deposition (PVD) or CVD, un-doped silicon glass (USG) or poly-Si is deposited by chemical vapor deposition (CVD), the thickness of the film before and after etching is measured by an n&k analyzer. Etching the high k film with H₂SO₄ at 160

, the etch rate is 1.15

5.25A/min and the selectivity to USG is 1:1, can be acceptable, but high temperature endurable wet bench is needed. Etching with pure phosphoric acid (H₃PO₄), pure perchloric acid (HClO₄), pure hydrochloric acid (HCl), pure hydro bromide (HBr), pure hydroiodide (HI) or pure acitic acid (COOH)₂, the etch rate is too low and can not be used. Etching with dilute hydrochloric (HF:H₂O=1:2000), the etch rate of HfO₂ is 1A/min, but the etch rate of USG is as high as 7A/min., the selectivity of 1:7 can not be acceptable, it will damage the USG in the shallow trench isolation region. Using a mixture of HF and HClO₄ at low temperature with volume ratio of 1:50 to 1:5000, the etch rate is above 10A/min. with increasing HClO₄, the etch rate of USG is decreasing slowly, at volume ratio of 1:2000, the selectivity can approach 1:0.65 (HfO₂:USG) as shown in FIG. 3 and FIG. 4. FIG. 3 shows the selectivity curve of HfO₂ to USG when etching with a mixture of HF and HClO₄ with different volume ratio. The selectivity is increase from HfO₂:USG=1:66=0.015 to 1:0.65=1.54. FIG. 4 is the etch rate of HfO₂ using different volume ratio of HF:HClO₄ increasing from 1:5 to 1:2000, the etch rate of HfO₂ keep at a constant value above 10A/min., but to USG or poly-Si, the etch rate is below 10A/min. The results show that etching high k film HfO₂ at low temperature (0

100

) can get acceptable etch rate of 10A/min, and will not damage the USG on the STI region, the poly-Si, metal, refractory metal or silicide on the gate, or the poly-Si, BPSG or PSG on the lower electrode of a capacitor, and need not use high temperature endurable wet bench and suitable for mass production. At low temperature (0

1001

), with volume ratio of HF:HClO₄=1:50 to 1:5000, the etch rate of HfO₂ is acceptable and the selectivity to wet oxide, USC, BPSG or poly-Si is high enough for production, the best volume ratio is 1:1000 to 1:2500.

[0033] Etching can be carried out by using single wafer tools, batch type tools, clusters tools, or stand alone tools. Etching is not limited to a special tool, any tool which make the HF and the HClO₄ contact with the wafer can be used.

[0034] In addition, it is equivalent to replace the perchloric acid (HClO₄) with perbromic acid (HBrO₄), periodic acid (HIO₄), so the mixture is not limited to HF:HClO₄, but HF:HBrO₄ or HF:HIO₄ can be used.

[0035] Second Embodiment

[0036] Refer to FIG. 5 to FIG. 15, which shows the process step of the manufacturing method of a CMOS 200. It is especially emphasis on the formation step and method of a high k gate. FIG. 5 shows the structure of a CMOS logic device 200. In the following description the silicon substrate is p-type, but n-type substrate or SOI (silicon on insulator) substrate can be used. The isolation of the second embodiment using shallow trench isolation is an example, but LOCOS isolation can be used. Tungsten silicide on poly-Si gate is used to reduce the gate resistance, but salicide like TiSi₂ or CoSi₂ can be used to replace WSi_(x). Also the gate is not limited to poly-Si gate, such as metal gate or refractory metal silicide can be used. The CMOS integration process which include the use of high k material should be included in the present invention.

[0037] In step of FIG. 6, the active area is defined by selectively formed the device isolation STI on the p-type silicon substrate, then forms the p-well 2 and n-well 3 by lithography and ion implantation, therein the p-well region will be the NMOS area and the n-well region will be the PMOS area. Then in step of FIG. 7, high k film 5 (i.e. HfO₂ or ZrO₂) of gate dielectric is formed on the silicon substrate, then poly-Si 6 is deposited to form the poly silicon gate.

[0038] In step of FIG. 8, mask photo-resist PR1 is formed by lithography on the n-well region 3, then n-type dopant (As⁺ or P⁺) is implanted into the poly silicon 6 on the p-well region 2 to form N⁺ low resistance poly silicon 6 a.

[0039] After removed the photo-resist PR1 as shown in FIG. 9, mask photo-resist PR2 is formed on the p-well region 2, p-type dopant (B⁺ or BF₂ ⁺) is implanted into the poly-silicon 6 on the n-well region 3 to form p⁺ poly silicon 6 b.

[0040] After removed the photo-resist PR2, in step of FIG. 10, WSi_(x) is deposited on the poly silicon 6 a and 6 b to form a low resistance gate. But WSi_(x) can be replaced by self-aligned silicide which is formed together with the source/drain salicide.

[0041] In step of FIG. 1, a gate pattern photo resist is formed on the tungsten silicide 7, then selectively etch the tungsten silicide 7 and poly silicon 6 to form the gate tungsten silicide 7 a and 7 b and gate poly silicon 6 c and 6 d to form gates 9 a and 9 b.

[0042] In step of FIG. 12, photo resist PR3 is formed by lithography on the n-well 3, using PR3 and the gate 9 a as mask, lowly doped (1×10¹³

1×10¹⁴ cm⁻²) of n-type dopant (As⁺ or p⁺) is implanted into the p-well region to form n⁻ source/drain 10.

[0043] After removed the photo-resist PR3, as shown in FIG. 13, photo resist PR4 is form on the p-well region 2, using PR4 and the gate 9 b as mask, lowly doped (1×10¹³

1×10¹⁴ cm⁻²) of p-type dopant (B⁺) is implanted into the n-well region 3, to form p⁻ source/drain 11.

[0044] After removed the photo-resist PR4, a silicon nitride film is deposited, then anisotropic etching is used to form silicon nitride side-wall 8 as shown in FIG. 14. Now the high k film 5 is exposed except under the gates 9 a, 9 b and the side-wall 8.

[0045] In step of FIG. 15, using HF and HClO₄ (or HBrO₄, HIO₄) as the etch solution, the gates 9 a and 9 b, side-wall 8 as mask, remove the high k film above the source/drain and isolation region by wet etching at low temperature (0

100

). The volume ratio of the HF:HClO₄ mixture is 1:50 to 1:5000, the better is 1:1000 to 1:2500. It is simple than etching by hot sulfuric acid (HSO₄). It need not high temperature endurable equipment, the etch rate is faster, and will not damage the surface of silicon and silicon dioxide (USG or wet oxide) that the leakage current is lower and the topology of the wafer is smooth.

[0046] The gate process is then completed, the following process is well known. For example, forming LDD by ion implantation of n⁺ and p⁺ to the source/drain region; forming salicide such as TiSi₂ or CoSi₂ on the source/drain, if WSi_(x) has not used, the salicide will form on the poly-Si gate in this step. Then complete the back-end process of metallization to complete the CMOS logic device as shown in FIG. 5.

[0047] Third Embodiment

[0048]FIG. 16 is a cross section view of a DRAM having high k dielectric insulator (HfO₂ or ZrO₂) after forming a stack lower electrode of the capacitor and having deposited high k film (HfO₂ or ZrO₂) according to the present invention. After forming a shallow trench isolation 4 on the p-well 2, LDD source/drain (or n⁺ source/drain instead of LDD), gate 9, inter layer dielectric (ILD) 15, tungsten or poly-Si plug 17, BPSG inter metal dielectric (IMD) 16, silicon nitride etching stop layer 19 and lower electrode 21, then high k film 22 of the capacitor dielectric is deposited using PVD or CVD as shown in FIG. 16. The shape of the lower electrode is not limited to this stack type, other stack or trench capacitor can be used.

[0049] Then, as shown in FIG. 17, etch the high k film using HF and HClO₄ (or HBrO₄, HIO₄) as the etch solution and photo-resist PR5 as the protection mask to protect the lower electrode and the high k film on the electrode, in an etching tool by wet etching at low temperature (0

100

), to remove the high k film outside the lower electrode. The volume ratio of the mixture of HF:HClO₄ is 1:50 to 1:5000, the better is 1:1000 to 1:2500. It is simple than etching by hot sulfuric acid (H₂SO₄). It need not high temperature endurable equipment, the etch rate is faster, and will not damage the BPSG of the inter metal dielectric 16 that the leakage current is lower and the topology of the wafer is smooth.

[0050] Then the following process step (not shown) such as deposition of the poly-Si top electrode 23 and another IM layer 24, grounding the capacitor from the top electrode by a via hole 25 to the bonding pad 26, as shown in FIG. 17 are very simple to those skill in IC technology, will not describe further.

[0051] Fourth Embodiment

[0052] The other embodiment of the present invention is the application of a high k capacitor. Deposited a high k film as the dielectric of the capacitor on the substrate which having formed the lower electrode of the capacitor, then by using lithography to form a protection photo-resist to protect the high k film on the lower electrode, etch the high k dielectric at low temperature (0

100

) with a mixture of HF:HClO₄ (or HBrO₄, HIO₄). After that, deposited the top electrode and complete the following metallization process. High quality etching of the high k film can be achieved.

[0053] The above described embodiment intended to illustrate the present invention, not to limit the scope of the present invention, various embodiments and changes can be made thereonto without departing the broad spirit and scope of the invention, or application on other device etching within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention. 

What is claimed is:
 1. A method of high dielectric film wet etching, comprising the steps of: Preparing a wafer having deposited a high dielectric film on silicon dioxide or poly-silicon; Etching the high dielectric film with an etching agent by wet etching; Rinsing the wafer with de-ionized water; Drying the wafer;
 2. A method of manufacturing a CMOS logic device with high dielectric gate, comprising the steps of: Forming un-doped silicon glass (USG) in the shallow trench isolation or LOCOS, p-well and n-well region; Deposition of a high dielectric film and forming a conductive layer of the gate; Defining the gate pattern by lithography and etch the conductive layer outside the gate area; Implanting an n⁻ and p⁻ dopant in the p-well and n-well to form a lightly doped in the source/drain region; Deposition of a silicon nitride film and etching an isotropically to form a pair of silicon nitride side-walls; Etching the high dielectric film to removed the high dielectric on the source/drain region by using an etching agent by wet etching; Forming the highly doped source/drain by self aligned ion implantation using the gate and the side-wall as a mask; Completing the back-end metalization process.
 3. A method of manufacturing a high dielectric capacitor DRAM, comprising the steps of: Forming transistors and lower electrode of a capacitor of a DRAM on a wafer, depositing high dielectric film as the insulating film of the capacitor; Using lithography to form a photo resist pattern to protect the lower electrode and the high dielectric film on the lower electrode, then etch at low temperature to remove the high dielectric outside the lower electrode using an etching agent by wet etching; Depositing a top electrode; Completing the back-end metallization process.
 4. A method of manufacturing a high dielectric capacitor, comprising the steps of: Forming a lower electrode of a capacitor on a substrate, depositing a high dielectric film on the lower electrode as the insulating film of the capacitor; Using lithography to form a photo-resist pattern to protect the lower electrode and the high dielectric on the lower electrode, then etch at low temperature to remove the high dielectric outside the lower electrode using an etching agent by wet etching; Depositing a top electrode; Completing the back-end metallization process.
 5. A method according to claim 1,2,3 or 4, wherein the high dielectric film is Hafnium oxide (HfO₂)
 6. A method according to claim 1,2,3 or 4, wherein the high dielectric film is Zirconium oxide (ZrO₂).
 7. A method according to claim 1,2,3 or 4, wherein the etching agent is a mixture of hydrofluoric acid (HF) and perchloric acid (HClO₄).
 8. A method according to claim 1,2,3 or 4, wherein the etching agent is a mixture of hydrofluoric acid (HF) and perbromic acid (HBrO₄).
 9. A method according to claim 1,2,3 or 4, wherein the etching agent is a mixture of hydrofluoric acid (HF) and periodic acid (HIO₄).
 10. A method according to claim 7,8 or 9, wherein the mixture has a volume ratio of HF:HClO₄ (HBrO₄, HIO₄)=1:50 to 1:5000.
 11. A method according to claim 7,8 or 9, wherein the mixture has a volume ratio of HF:HClO₄ (HBrO₄,HIO₄)=1:1000 to 1:2500.
 12. A method according to claim 1,2,3 or 4, wherein etching is performed at low temperature (0

100

).
 13. A method according to claim 1,2,3 or 4, wherein etching is performed in a single wafer tool.
 14. A method according to claim 1,2,3 or 4, wherein etching is performed in a batch type tool.
 15. A method according to claim 1,2,3 or 4, wherein etching is performed in a clusters tool.
 16. A method according to claim 1,2,3 or 4, wherein etching is performed in a stand alone tool.
 17. A method according to claim 1,2,3 or 4, wherein the etch rate of HfO₂ of the etching agent is above 10A/min.
 18. A method according to claim 1,2,3 or 4, wherein the etch rate of ZrO₂ of the etching agent is above 10A/min.
 19. A method according to claim 1,2,3 or 4, wherein the etch rate of SiO₂ of the etching agent is below 10A/min.
 20. A method according to claim 1,2,3 or 4, wherein the etch rate of the undoped silicon glass (USG) of the etching agent is below 10A/min.
 21. A method according to claim 1,2,3 or 4, wherein the etch rate of BPSG of the etching agent is below 10A/min.
 22. A method according to claim 1,2,3 or 4, wherein the etch rate of PSG of the etching agent is below 10A/min.
 23. A method according to claim 1,2,3 or 4, wherein the etch rate of poly-Si of the etching agent is below 10A/min.
 24. A method according to claim 1,2,3 or 4, wherein the etch rate of Si of the etching agent is below 10A/min. 